The Federal Role in Groundwater Supply




The Federal Role in Groundwater Supply
Updated May 22, 2020
Congressional Research Service
https://crsreports.congress.gov
R45259




The Federal Role in Groundwater Supply

Summary
Groundwater, the water in aquifers accessible by wells, is a critical component of the U.S. water
supply. It is important for both domestic and agricultural water needs, among other uses. Nearly
half of the nation’s population uses groundwater to meet daily needs; in 2015, about 149 million
people (46% of the nation’s population) relied on groundwater for their domestic indoor and
outdoor water supply. The greatest volume of groundwater used every day is for agriculture,
specifically for irrigation. In 2015, irrigation accounted for 69% of the total fresh groundwater
withdrawals in the United States. For that year, California pumped the most groundwater for
irrigation, followed by Arkansas, Nebraska, Idaho, Texas, and Kansas, in that order. Groundwater
also is used as a supply for mining, oil and gas development, industrial processes, livestock, and
thermoelectric power, among other uses.
Congress generally has deferred management of U.S. groundwater resources to the states, and
there is little indication that this practice will change. Congress, various states, and other
stakeholders recently have focused on the potential for using surface water to recharge aquifers
and the ability to recover stored groundwater when needed. Some see aquifer recharge, storage,
and recovery as a replacement or complement to surface water reservoirs, and there is interest in
how federal agencies can support these efforts. In the congressional context, there is interest in
the potential for federal policies to facilitate state, local, and private groundwater management
efforts (e.g., management of federal reservoir releases to allow for groundwater recharge by local
utilities).
The two primary federal water resources agencies are the U.S. Bureau of Reclamation
(Reclamation) and the U.S. Army Corps of Engineers (USACE). No significant federal
restrictions apply to Reclamation’s authorities to deliver water for purposes of aquifer recharge,
storage, and recovery. USACE authorities also do not restrict nonfederal entities from using water
stored or released from USACE reservoirs for groundwater recharge. Both agencies acknowledge
that some state restrictions affect the use of the delivered or stored waters for groundwater
activities. Reclamation, the U.S. Department of Agriculture (USDA), and the U.S. Environmental
Protection Agency also provide some forms of financial assistance that could be used for
enhancing groundwater supplies.
Other federal agencies support activities that inform groundwater management. For example, the
U.S. Geological Survey monitors and reports groundwater conditions across the country, develops
groundwater models and software tools for characterizing aquifers, and provides long- and short-
term forecasts of changing groundwater conditions as part of local and regional groundwater
studies. The National Aeronautics and Space Administration and the National Oceanic and
Atmospheric Administration also make observations and collect data that are relevant to
groundwater monitoring and assessment. USDA collects groundwater data related to irrigation.
Long-term changes to the climate affecting the United States, particularly rising temperatures and
changes in the patterns, quantities, and type of precipitation (i.e., rain versus snow), could affect
the availability of groundwater in the future. Other factors, such as changes to land use, irrigation
practices, and patterns of water consumption, also may influence future changes to groundwater
supplies.

Congressional Research Service

link to page 6 link to page 6 link to page 6 link to page 7 link to page 8 link to page 8 link to page 8 link to page 9 link to page 9 link to page 10 link to page 10 link to page 11 link to page 11 link to page 16 link to page 17 link to page 17 link to page 19 link to page 20 link to page 20 link to page 21 link to page 22 link to page 24 link to page 26 link to page 27 link to page 28 link to page 28 link to page 29 link to page 31 link to page 32 link to page 7 link to page 12 link to page 13 link to page 14 link to page 15 link to page 16 link to page 16 link to page 18 link to page 19 link to page 22 The Federal Role in Groundwater Supply

Contents
Overview ......................................................................................................................................... 2
Who Relies on Groundwater? ................................................................................................... 2
Groundwater and Irrigation ....................................................................................................... 2
The Federal Role in Groundwater Supply ................................................................................. 3
Congressional Interest ............................................................................................................... 4
Groundwater Recharge, Storage, and Recovery ....................................................................... 4

Background ......................................................................................................................... 4
Groundwater Rights .................................................................................................................. 5
Background ......................................................................................................................... 5
Groundwater Monitoring .......................................................................................................... 6
Background ......................................................................................................................... 6
Primer on Groundwater ................................................................................................................... 7
Types of Aquifers ...................................................................................................................... 7
Federal Activities and Authorities ................................................................................................. 12
Groundwater Monitoring and Assessment .............................................................................. 13
U.S. Geological Survey ..................................................................................................... 13
NASA ................................................................................................................................ 15
NOAA ............................................................................................................................... 16
USDA ................................................................................................................................ 16

Federal Authority Related to Groundwater Recharge, Storage, and Recovery ....................... 17
Bureau of Reclamation ..................................................................................................... 18
U.S. Army Corps of Engineers ......................................................................................... 20
USDA ................................................................................................................................ 22
U.S. Environmental Protection Agency ............................................................................ 23
Federal Reserved Rights to Groundwater ............................................................................... 24
Climate Change and Other Long-Term Influences on Groundwater Supply ................................ 24
Climate Change and Groundwater Recharge .......................................................................... 25
Other Factors ........................................................................................................................... 27
Summary and Conclusions ............................................................................................................ 28

Figures
Figure 1. Groundwater Withdrawals for Irrigation (2015) .............................................................. 3
Figure 2. Unconfined, or Water Table, Aquifer ............................................................................... 8
Figure 3. Different Types of Aquifers and Wells ............................................................................. 9
Figure 4. Unconfined Aquifer Without Pumping (top) and With Pumping (bottom) .................... 10
Figure 5. Water Level Changes in the High Plains Aquifer, Predevelopment to 2007 ................... 11
Figure 6. Land Subsidence in the San Joaquin Valley Southwest of Mendota Between
1925 and 1977 ............................................................................................................................ 12
Figure 7. Below-Normal Groundwater Levels for Actively Monitored Wells .............................. 14
Figure 8. Shallow Groundwater and Soil Moisture Comparison from NASA Satellite Data ....... 15
Figure 9. Groundwater Recharge, Storage, and Recovery ............................................................ 18
Congressional Research Service

link to page 31 link to page 31 link to page 33 The Federal Role in Groundwater Supply

Figure 10. Conceptual Illustration of Recharge Mechanisms Under Two Different
Climate Scenarios ....................................................................................................................... 27

Contacts
Author Information ........................................................................................................................ 29


Congressional Research Service

The Federal Role in Groundwater Supply

roundwater, the water in aquifers accessible by wells, is a critical component of the U.S.
water supply. It serves as a water source for domestic use and as irrigation water for
G agriculture, and it is used in mining, oil and gas development, industrial processes,
livestock production, and thermoelectric power generation, among other uses. Managing
groundwater resources largely has been the purview of states rather than the federal government.
How each state manages its groundwater resources differs and depends on a mix of common law
emerging from the 19th century, state law, court decisions, water settlements, and, to a lesser
extent, federal law. The federal role in managing groundwater includes activities under federal
trust responsibilities to Indian tribes and reservations.1 It also includes management
responsibilities for certain federal reservations if the purposes of those reservations require water,
such as some national monuments, national forests, military bases, and other federal land
holdings. In addition, the federal government is involved in groundwater monitoring and
assessment and in aspects of groundwater recharge, storage, and recovery. Much of the recent
congressional interest in groundwater has been broadly related to policies for increasing water
supplies generally, as a response to recent droughts, and in preparation for future droughts.
In recent Congresses, some Members have introduced legislation that could affect how
groundwater resources may be managed to better ensure a sufficient and reliable supply, and
several such bills (or portions of such bills) have been enacted into law. Drought conditions and
constrained supplies of surface water have helped to spur legislative action.2 These conditions
continue to affect many regions in western states, although droughts can occur anywhere in the
nation.3 Congress could continue to explore its authority to shape policy, conduct oversight, and
provide appropriations for federal activities that influence groundwater supply management in the
United States. This report is intended to provide context and a broad summary of federal
authorities and activities affecting the supply and use of groundwater resources.
Whereas the states primarily manage groundwater supply, the federal government plays a more
direct role in managing the nation’s groundwater quality. For example, the Comprehensive
Environmental Response, Compensation, and Liability Act (42 U.S.C. §§9601 et seq.) authorizes
federal cleanup and enforcement actions to respond to releases of hazardous substances to the
environment, including groundwater. In addition, the Safe Drinking Water Act (42 U.S.C. §§300f
et seq.) authorizes the U.S. Environmental Protection Agency (EPA) to regulate underground
injection activities to protect underground sources of drinking water, including injection wells
used for aquifer recharge. This report focuses on issues related to groundwater supply, not
groundwater quality.4
This report is divided into two parts. The first part provides an overview of groundwater supply
and management, including selected major issues before Congress. The second part provides a
more detailed primer on groundwater resources, including relevant federal activities and
authorities.

1 Unless otherwise noted, the terms Indian, Indian tribes, and tribal reservations refer to the approximately 1.9 million
American Indians and Alaska Natives, the more than 570 federally recognized Indian tribes, and tribal land within
reservation boundaries.
2 Surface water includes streams, rivers, lakes, ponds, and is not groundwater or atmospheric water like rain or snow.
3 For a general overview of drought in the United States, see CRS Report R43407, Drought in the United States:
Causes and Current Understanding
, by Peter Folger.
4 Many CRS resources address issues of groundwater quality, including CRS Report R41039, Comprehensive
Environmental Response, Compensation, and Liability Act: A Summary of Superfund Cleanup Authorities and Related
Provisions of the Act
, by David M. Bearden; and CRS Report RL31243, Safe Drinking Water Act (SDWA): A Summary
of the Act and Its Major Requirements
, by Mary Tiemann.
Congressional Research Service

1

link to page 7 The Federal Role in Groundwater Supply

Overview
Who Relies on Groundwater?
Nearly half of the U.S. population relies on groundwater to meet their everyday needs. In 2015,
groundwater was the primary source of water for domestic indoor and outdoor water uses for
about 149 million people (46% of the U.S. population).5 Most U.S. citizens (approximately 282
million people, or 87%) depended on public water supplies in 2015.6 The remaining 13%
(approximately 42.5 million people) supplied their own water, and nearly all of these citizens
(98%, or about 42 million) pumped the water from their private wells. About 38% of public
supply water is groundwater, and about 107 million people used groundwater from public water
supplies.7 Combined with the 42 million people pumping groundwater from their private wells,
an estimated 149 million people relied on groundwater in 2015.
Groundwater and Irrigation
The greatest volume of groundwater used is for agriculture, nearly entirely for irrigation. In 2015,
irrigation accounted for over 69% of all fresh groundwater withdrawals in the United States,8
which corresponded to about 57.2 billion gallons per day (bgpd) in irrigation withdrawals as
compared to 18.4 bgpd in withdrawals for domestic use (both public supply and self-supplied
groundwater—in total, about 22% of all fresh groundwater withdrawals).9 Among all states,
California uses the most groundwater for irrigation, withdrawing 13.9 bgpd in 2015. Arkansas is
second, withdrawing 9.28 bgpd in the same year, followed by Nebraska (5.42 bgpd), Idaho (4.9
bgpd), Texas (4.48 bgpd), and Kansas (2.56 bgpd).10 Overall, groundwater withdrawals for
irrigation in 2015 accounted for 48% of the total water withdrawn for irrigation, an increase of
16% compared to 2010.11 In comparison, surface water sources supplied 52% of total irrigation
withdrawals, a decrease of about 8% from 2010.12
Figure 1 illustrates the amount of groundwater withdrawn for irrigation by state. Generally,
western states tend to use the most groundwater, due in part to hydrology and other surface water
supply constraints.

5 Cheryl A. Dieter and Molly A. Maupin, Public Supply and Domestic Water Use in the United States, 2015, U.S.
Geological Survey (USGS), Open-File Report 2017-1131, 2017, at https://doi.org/10.3133/ofr20171131. (Hereinafter,
Dieter and Maupin, 2017.)
6 Public water supply, as used in USGS reports and herein, refers to water withdrawn by public and private water
suppliers that provide water to at least 25 people or have a minimum of 15 connections. It excludes self-supplied
domestic withdrawals.
7 Dieter and Maupin, 2017.
8 Cheryl A. Dieter et al., Estimated Use of Water in the United States in 2015, USGS, Circular 1441, 2018, at
https://pubs.er.usgs.gov/publication/cir1441. (Hereinafter, Dieter et al., 2018.) 2015 is the most recent year for which
these data are available. Nearly all groundwater withdrawals in 2015 were freshwater (about 97%); the remainder (3%)
were saline water withdrawals.
9 Irrigation, public supply, and self-supplied groundwater withdrawals accounted for about 92% of the total fresh
groundwater pumped in 2015. The remaining 8% included uses for livestock, aquaculture, industrial, mining, and
thermoelectric power. Dieter et al., 2018, Table 4a.
10 Dieter et al., 2018, Table 7.
11 Dieter et al., 2018, p. 28.
12 Dieter et al., 2018, p. 28.
Congressional Research Service

2

link to page 16
The Federal Role in Groundwater Supply

Figure 1. Groundwater Withdrawals for Irrigation (2015)

Source: Cheryl A. Dieter et al., Estimated Use of Water in the United States in 2015, USGS, Circular 1441, 2018,
at https://pubs.er.usgs.gov/publication/cir1441, p. 29, figure 7. (Modified by CRS.)
The Federal Role in Groundwater Supply
The federal government directly and indirectly influences how groundwater is managed in the
United States. Several federal agencies monitor groundwater directly or with partners—through
measurements at wells and springs—and remotely, using satellites or other remote sensing
devices to provide information on groundwater flow, storage, depletion, and other characteristics
that help inform state and local groundwater management. These include the U.S. Geological
Survey (USGS), the National Aeronautics and Space Agency (NASA), the National Oceanic and
Atmospheric Administration (NOAA), and the U.S. Department of Agriculture (USDA).13
Congress has provided other federal agencies with the authority to make available some water
delivered from or stored at federal water resource projects available for groundwater recharge,
storage, and recovery. These agencies include the two principal federal water resources agencies:
the U.S. Army Corps of Engineers (USACE, which operates nationwide) and the U.S. Bureau of
Reclamation (Reclamation, which operates in the 17 coterminous states west of the Mississippi
River). Additionally, courts have found that when the federal government reserves lands for a
particular purpose (such as for a tribal reservation or national monument), it impliedly reserves a
right to water necessary to accomplish the purposes for which the reservation was created. Thus,
federal land management agencies and the Bureau of Indian Affairs often are involved in water
rights issues. Federal reserved water rights doctrine has long been recognized for surface water;
more recently, it is also being considered for groundwater.

13 For more information on the roles of the agencies, see the below section, “Federal Activities and Authorities.”
Congressional Research Service

3

link to page 21 link to page 21 link to page 21 link to page 21 The Federal Role in Groundwater Supply

Congressional Interest
In recent years, congressional interest in groundwater has generally been in three major areas:
 aquifer storage, recharge, and recovery;
 groundwater rights (including among other issues, groundwater/surface water
interaction and federal reserved water rights); and
 groundwater supply monitoring and assessment.
In some cases, these issues overlap.
Groundwater Recharge, Storage, and Recovery
Background
Historically, the federal government, through USACE and Reclamation, has played a prominent
role in constructing infrastructure related to surface water resource management (e.g., storage,
control, or delivery). At the same time, the federal government has played a comparatively
smaller role in creating infrastructure to develop groundwater storage, which is commonly
conducted as aquifer storage, recovery, and/or recharge.14 The reasons for the differing levels of
federal involvement are complex, tied to the long and complicated history of common law water
rights, state water law, legal adjudication, federal deference to states on water supply issues, and a
historically cruder understanding of how groundwater occurs and moves underground compared
to surface water.
Both public and congressional focus on groundwater storage has sharpened in recent years,
particularly in reaction to recent major drought events. Congressional interest has increased in the
potential for the federal government to assist with state, local, and private groundwater
management efforts, including efforts to use surface water to recharge and/or store water in
aquifers and to recover (i.e., pump to the surface) the stored groundwater when needed. Some see
aquifer recharge, storage, and recovery as potentially complementary to existing surface water
storage; some also see these projects as possible alternatives to building new surface water
reservoirs that may prove less costly and/or pose fewer environmental issues.15
Federal law authorizes Reclamation to provide water for irrigation and USACE to store water for
various purposes. These authorities provide some opportunities for the federal government to
promote aquifer recharge, storage, and recovery (see below section, “Federal Authority Related to
Groundwater Recharge, Storage, and Recovery”)
. Currently, there are no general federal
restrictions on the nonfederal use of water delivered by Reclamation or stored by USACE for
aquifer recharge, storage, and recovery purposes; however, some state restrictions and federal
environmental protection laws may affect the use of these waters for groundwater recharge.16

14 For more background on this concept, see the below section, “Federal Authority Related to Groundwater Recharge,
Storage, and Recovery.”

15 An example of a major aquifer storage project currently operating within a larger water storage framework is the
Kern Water Bank, a water storage bank that operates on about 20,000 acres southwest of Bakersfield, California. As of
2018, the bank could store about 1.5 million acre-feet of readily available water underground, with the ability to
recover approximately 240,000 acre-feet within a 10-month period. Since its construction in 1996, the bank has formed
an important component of California’s water storage network. For more information, see http://www.kwb.org/
index.cfm/fuseaction/Pages.Page/id/330.
16 For example, injection wells used for aquifer recharge or aquifer storage and recovery require a permit under the
federal Safe Drinking Water Act (42 U.S.C. §300h). For further information, see https://www.epa.gov/uic/aquifer-
Congressional Research Service

4

link to page 24 link to page 24 The Federal Role in Groundwater Supply

Although Congress has authorized aquifer storage, recharge, and/or recovery for some individual
projects, general congressional guidance in this area has been limited. Under the Water
Infrastructure Improvements for the Nation Act (WIIN Act; P.L. 114-322), Congress provided
general authority for Reclamation to support new and enhanced federal and state surface and
groundwater storage projects under certain, limited circumstances.17 Reclamation, USDA, and
EPA also provide some forms of financial assistance that could support aquifer recharge, storage,
and recovery.
Groundwater Rights
Background
Groundwater and Surface Water Interaction
One reason often cited for the evolution of different legal frameworks for groundwater and
surface water in most states is the relative lack of understanding of groundwater occurrence and
movement in the 19th and early 20th centuries, when states and courts first established laws and
rules allocating groundwater. Surface water was more readily understood, being in plain view, but
groundwater was considered different and mysterious, being largely unobservable except at the
bottom of a well. One commentator noted that the development of groundwater common law in
England and the United States in the 19th century was “steeped in ignorance,”18 as groundwater
hydrology and hydraulics were virtually unknown compared to surface water. Citing a legal case
from 1861 referring to groundwater, the commentator said,
the existence, origin, movement and course of such waters, and the causes which govern
and direct their movements, are so secret, occult and concealed, that an attempt to
administer any set of legal rules in respect to them would be involved in hopeless
uncertainty, and would be, therefore, practically impossible.19
Groundwater science has made significant strides in the interim, particularly in establishing the
interconnected nature of surface water and groundwater in many instances, especially for shallow
aquifers. Some observers argue that groundwater law has not kept pace in some cases, in part
because of the courts’ reluctance to unsettle a system of common law established under the
principle of property rights; observers note that a disruption of this system could result in legal
chaos.20
The complicated nature of groundwater laws and practices is noteworthy because any new
executive branch action or federal legislation authorizing action that affects groundwater
resources may perturb long-established state and local groundwater management regimes. The
practice of managing groundwater and surface water together, termed conjunctive management,
better reflects the intertwined nature of groundwater and surface water in many situations and is

recharge-and-aquifer-storage-and-recovery.
17 For more information, see below section, “Reclamation Authority to Provide Financial Support for Groundwater
Storage.”

18 Joseph W. Dellapenna, “A Primer on Groundwater Law,” Idaho Law Review, vol. 49, no. 265 (2013), p. 267.
Hereinafter Dellapenna, 2013.
19 Dellapenna, 2013, citing Frazier v. Brown, 12 Ohio St. 294, 311 (1861).
20 Dellapenna, 2013, p. 268.
Congressional Research Service

5

link to page 16 The Federal Role in Groundwater Supply

generally recognized as an effective management approach, especially for shallow aquifers. Yet,
groundwater law sometimes does not reflect or address that surface-groundwater interconnection.
Federal Reserved Water Rights
Federal reserved water rights doctrine is an important concept in groundwater law. This doctrine
holds that when the federal government reserves lands for a particular purpose (such as for a
tribal reservation or national monument), the government impliedly reserves a right to water
necessary to accomplish the primary purpose for which the reservation was created.21 Since 1908,
when the Supreme Court established the doctrine in Winters v. United States, courts have applied
this doctrine to surface waters.22 A March 2017 decision of the U.S. Court of Appeals for the
Ninth Circuit (Ninth Circuit) held, for the first time, that the doctrine can encompass groundwater
as well.23
Congress has recently been involved in Indian water rights settlements, chiefly regarding tribal
rights to surface water supplies and the appropriation of funds for enacted settlement agreements.
The importance of groundwater to tribal water supplies is increasingly being discussed, and tribal
rights to groundwater are the subject of ongoing litigation.24
Groundwater Monitoring
Background
Although the states have assumed primary responsibility for groundwater management, several
federal agencies monitor, forecast, and assess groundwater conditions in the United States.25 One
agency, USGS, within the Department of the Interior (DOI), is a science agency with no
regulatory or management responsibilities for water resources. For decades, USGS has monitored
and reported groundwater conditions across the country; developed groundwater models and
software tools for characterizing aquifers; and provided long- and short-term forecasts of
changing groundwater conditions as part of local and regional groundwater studies.26 The
information is used to support federal, state, and local decisionmakers, and the research is often
conducted in collaboration with federal, state, and local partners. For example, USGS makes data
from its distributed water database available to stakeholders. The database is a locally managed
network of stations that monitor surface-water flow, groundwater levels, and water quality across

21 See, for example, the U.S. Department of Justice, “Federal Reserved Water Rights and State Law Claims,” at
https://www.justice.gov/enrd/federal-reserved-water-rights-and-state-law-claims. The nature of the water right for a
specific federal reservation depends on various aspects of the reservation, such as its purpose and the mechanism for
the reservation; the discussion herein is intended to introduce the topic of groundwater rights related to federal
reservations generally and is not intended to clarify how the specific rights related to a reservation are determined. For
example, in some cases, Congress has expressly not reserved water rights.
22 Winters v. United States, 207 U.S. 564, 575-77 (1908).
23 Agua Caliente Band of Cahuilla Indians v. Coachella Valley Water District, No. 15-55896 (9th Cir. 2017).
24 See, for example, CRS Insight IN10857, Federal Reserved Water Rights and Groundwater: Quantity, Quality, and
Pore Space
, by Peter Folger.
25 For more information on the roles of the agencies, see the below section, “Federal Activities and Authorities.”
26 USGS, “USGS Groundwater Information: USGS Groundwater Science for a Changing World,” at
https://water.usgs.gov/ogw/about/.
Congressional Research Service

6

link to page 12 link to page 12 The Federal Role in Groundwater Supply

the nation. The database includes long- and short-term records from more than 850,000
groundwater measurement sites.27
Other agencies, such as NASA and NOAA, make observations and collect data that also are
relevant to groundwater monitoring and assessment. Earth-observing satellites that detect changes
in gravity, for example, can help link those changes to losses or gains in the volume of
groundwater due to pumping or recharge. NOAA’s estimation of drought severity throughout the
country, as expressed in the U.S. Drought Monitor,28 includes the estimation of the effects of
drought on groundwater supplies. Also, USDA collects irrigation data, including information on
wells, characteristics of aquifers used for irrigation supply, and quantities of water applied from
wells.29
Primer on Groundwater
Groundwater science has advanced markedly in the last century; this primer presents an
introduction to fundamental concepts relevant to groundwater use, management, and recharge.
Groundwater is found in aquifers. An aquifer is composed of (1) solid materials, such as rocks
and mineral grains; (2) interconnected spaces or openings (pore space); and (3) groundwater,
which completely fills the pore space (Figure 2). Strictly speaking, an aquifer is sufficiently
permeable (i.e., groundwater can move readily through the interconnected pores) to transmit
economic quantities of water to wells or springs.30 In other words, if a farmer drills a well into a
water-bearing layer of rock or sediments (sometimes called a formation) and can pump sufficient
quantities of groundwater to irrigate crops, water livestock, or use for drinking water and
washing, then that formation can be considered an aquifer. If the same farmer drilled a well but
could not pump enough water to satisfy any needs, then the formation would not be considered an
aquifer.
Types of Aquifers
There are two principal types of aquifers: unconfined and confined. An unconfined aquifer is one
in which the water table moves up and down freely without an overlying confining layer (see
Figure 2).31

27 See, for example, USGS, “USGS Groundwater Watch,” at https://groundwaterwatch.usgs.gov/.
28 See United States Drought Monitor at http://droughtmonitor.unl.edu/.
29 The U.S. Environmental Protection Agency (EPA) plays a significant role in matters related to groundwater quality.
Such EPA authorities and activities are beyond the scope of this report.
30 C. W. Fetter, “Glossary,” in Applied Hydrogeology, 2nd ed. (Columbus, OH: Merrill Publishing Company, 1988), p.
565.
31 A confining layer is a bed or strata composed of relatively impermeable materials, such as clay, so that groundwater
flow through the layer is impeded or significantly restricted. The ability of a bed or strata to conduct groundwater flow
is referred to as hydraulic conductivity. A confining layer would have a low hydraulic conductivity compared to an
aquifer.
Congressional Research Service

7

link to page 13
The Federal Role in Groundwater Supply

Figure 2. Unconfined, or Water Table, Aquifer
(illustrating two types of pore space)

Source: USGS, USGS Water Science School, “Aquifers and Groundwater,” at https://water.usgs.gov/edu/
earthgwaquifer.html. (Modified by CRS.)
Notes: Above the water table, the pores may contain water but are not completely full. Only the saturated
zone below the water table is considered the aquifer.
A confined aquifer, in contrast, is an aquifer overlain (and sometimes underlain) by an
impermeable or confining layer that the water does not freely move above. The confining beds
cause the aquifer to be under pressure. As a result, when a well penetrates a confined aquifer, the
water will rise above the top of the aquifer, sometimes all the way to the land surface (the latter
case is referred to as an artesian aquifer), as shown in Figure 3.
Congressional Research Service

8

link to page 13 link to page 14 link to page 14
The Federal Role in Groundwater Supply

Figure 3. Different Types of Aquifers and Wells

Source: Government of Canada, Environment and Natural Resources, “Water Sources: Groundwater,” at
https://www.canada.ca/en/environment-climate-change/services/water-overview/sources/groundwater.html.
Notes: The piezometric surface in the figure refers to an imaginary line that corresponds to where the water
level in the confined aquifer would rise if not for the impermeable confining layer. It also corresponds to the
water level in the artesian wells shown in the figure.
The distinction between unconfined and confined aquifers is important for this discussion, as the
technique of groundwater recharge, storage, and recovery differs depending on what kind of
aquifer is involved. Because a confining layer or layers separates a confined aquifer from surface
water bodies, the degree of connection between surface water and groundwater is not as direct or
distinct as it is for unconfined aquifers.32 Groundwater recharge can occur naturally in confined
and unconfined aquifers as water moves downward from the land surface into the aquifer from
rain and melting snow, lakes, river, and streams. For unconfined aquifers, other sources of
recharge water can include built impoundments, such as reservoirs; unlined irrigation ditches and
canals; and applied irrigation water not consumed by crops. In a system of managed artificial
recharge
, water can be added deliberately to a confined or unconfined aquifer by using an
injection well; by spreading water across the land surface, where it can trickle down into an
unconfined aquifer; or by building an impoundment to temporarily store water and allow it to
leak through the bottom down to an unconfined aquifer.
The distinction between an unconfined and a confined aquifer also is important for understanding
the connection between surface water and groundwater. In Figure 3, the confined aquifer is
separated from the river by a confining layer, so that changes in river flow will not directly affect
groundwater in the confined aquifer and flow from the artesian wells will not directly affect flow
in the river. In Figure 4, by contrast, the unconfined aquifer is connected directly to the stream.
Under natural conditions, the groundwater will flow toward and feed the stream (top panel)
because the slope of the water table is toward the top of the stream level. However, sometimes
when aquifers are subject to excessive pumping—during drought conditions, for example, or
because of a lack of surface water availability—they are said to be under stress. Under stressed
conditions (bottom panel of Figure 4), pumping from a well will cause the water table to slope

32 Decades of groundwater development involving hundreds or thousands of wells in some agricultural regions of the
United States, such as California’s Central Valley, sometimes have led to interconnections between the unconfined and
confined aquifers. Wells penetrating the confining layer above the confined aquifers can serve as conduits for
groundwater to flow up or down. See, for example, Claudia C. Faunt et al., Groundwater Availability of the Central
Valley Aquifer, California
, USGS, Professional Paper 1766, 2009, pp. 85-86.
Congressional Research Service

9

link to page 15 link to page 16
The Federal Role in Groundwater Supply

away from the top of the stream. In that case, the water in the stream will leak through the stream
bottom and flow into the aquifer, toward the pumping well.
Figure 4. Unconfined Aquifer Without Pumping (top) and With Pumping (bottom)

Source: Steven M. Gorelick and Chunmiao Zheng, “Global Change and the Groundwater Management
Challenge,” Water Resources Research, vol. 51, March 28, 2015 (with permission).
Notes: Under natural conditions in this particular case, groundwater flows toward the stream (arrows indicate
direction of groundwater flow) and the water table is high enough to be accessible to trees and plants. During
pumping, when the aquifer is stressed, water flows from the stream into the aquifer and toward the well. Also,
the water table under stressed conditions drops below the roots of trees and plants depicted in the figure,
affecting their growth.
Consistently stressed conditions can have dramatic long-term effects on groundwater. If pumping
continues in excess of recharge, increasing stress on the aquifer, the water table may drop tens to
hundreds of feet (Figure 5). This situation has occurred in many regions of the United States,
including the Ogallala aquifer (also called the High Plains aquifer) underlying several Midwest
and Great Plains states and in California’s Central Valley. In the Central Valley, historical levels
of pumping caused the water table to drop so far in some areas that it caused the land surface to
drop, or subside, nearly 30 feet (Figure 6). Excessive land subsidence can harm surface
structures, such as canals and levees.
Congressional Research Service

10


The Federal Role in Groundwater Supply

Figure 5. Water Level Changes in the High Plains Aquifer, Predevelopment to 2007

Source: V. L. McGuire, “Changes in Water Levels and Storage in the High Plains Aquifer, Predevelopment to
2007,” USGS, Fact Sheet 2009-3005, February 2009. (Modified by CRS.)
Note: Predevelopment refers to approximately 1950.
Congressional Research Service

11


The Federal Role in Groundwater Supply

Figure 6. Land Subsidence in the San Joaquin Valley Southwest of Mendota Between
1925 and 1977

Source: Devin Galloway et al., “Land Subsidence in the United States,” USGS Circular 1182, 1999, p. 23, at
http://pubs.usgs.gov/circ/circ1182/pdf/06SanJoaquinValley.pdf.
Note: Approximate location of the maximum land subsidence in the United States, showing the approximate
relative position of the land surface in 1925, 1955, and 1977.
Federal Activities and Authorities
The federal government directly and indirectly influences how groundwater is managed in the
United States. Several federal agencies monitor groundwater directly or with partners—through
measurements at wells and springs—and remotely, using satellites or other remote sensing
devices to provide information on groundwater flow, storage, depletion, and other characteristics
that help inform state and local groundwater management. These agencies include the USGS,
NASA, the National Oceanic and Atmospheric Administration, and USDA. Congress has
provided other federal agencies with the authority to make water delivered from or water stored at
federal water resource projects available for groundwater recharge, storage, and recovery. These
include the two principal federal water resources agencies: USACE (which operates nationwide)
and Reclamation (which operates in the 17 coterminous states west of the Mississippi River).
Reclamation, USDA, and EPA also provide some forms of financial assistance that could support
groundwater storage, recharge, and recovery.
Congressional Research Service

12

link to page 9 link to page 18 The Federal Role in Groundwater Supply

Additionally, when the federal government reserves lands for a particular purpose (such as for a
tribal reservation or national monument), it impliedly reserves a right to water necessary to
accomplish the purposes for which the reservation was created. That federal reserved water rights
doctrine has long been recognized for surface water; more recently, it is also being considered for
groundwater. (See discussion under “Groundwater Rights.”)
Groundwater Monitoring and Assessment
Several federal agencies that have no regulatory role in managing groundwater are authorized to
collect data, make observations and assessments, and provide information on groundwater
supplies that supports decisionmakers at the state and local levels. USGS likely provides the most
direct groundwater information and support for groundwater management among the federal
agencies, although NASA and NOAA also make pertinent observations and distribute
groundwater-relevant information. USDA also collects groundwater data related to irrigation.
Selected activities within those four agencies are briefly summarized below.
U.S. Geological Survey
The Groundwater and Streamflow Information Program, within the USGS water resources
mission area, funds activities that provide information directly relevant to groundwater
management. About 10% ($7.5 million in FY2019) of the approximately $74 million program is
directed at groundwater-related activities, including the National Groundwater Monitoring
Network (NGWMN).33 The NGWMN is a compilation of selected groundwater monitoring wells
from federal, state, and local monitoring networks across the country. Data from the network are
accessible through a portal that contains current and historical data.34 USGS administers the
program through cooperative agreements with state and local water resource agencies; in
FY2020, Congress provided $3.9 million to USGS to fund the network, the same as the enacted
amounts for the previous four years.35
USGS also maintains a distributed groundwater database, the USGS Groundwater Watch. It is
locally managed and contains data from more than 850,000 wells compiled over the past 100
years. The long-term and distributed nature of the data is valuable to groundwater managers
seeking information about regional groundwater trends over time. Figure 7 shows an example of
one of the products updated daily from groundwater well information within the database.

33 Email from Jeffrey Onizuk, USGS Congressional Affairs, March 19, 2020.
34 Advisory Committee on Water Information, “National Ground-Water Monitoring Network,” at https://cida.usgs.gov/
ngwmn/index.jsp.
35 Email from Jeffrey Onizuk, USGS Congressional Affairs, March 19, 2020.
Congressional Research Service

13


The Federal Role in Groundwater Supply

Figure 7. Below-Normal Groundwater Levels for Actively Monitored Wells
(data from 3,855 wells)

Source: USGS, “Groundwater Watch,” at https://groundwaterwatch.usgs.gov/net/ogwnetwork.asp?ncd=lwl.
(Modified by CRS.)
Notes: Below-normal means that the wells shown in red or orange had groundwater levels at the 24th
percentile or lower for the month the well was measured, compared to the entire period of record for the well.
In other words, if the well has been measured for 50 years, it would be shown on this map if the water level was
lower than 75% of the measurements taken over the past 50 years. Red dots indicate wells lower than the 10th
percentile; orange shows wells at the 10th-24th percentile.
In addition to collecting and providing data, USGS conducts regional groundwater studies, such
as assessing the groundwater availability in the Central Valley aquifer in California,36 and
national overviews, such as the Ground Water Atlas of the United States.37 Several observers have
suggested that although groundwater generally is locally managed in the United States, regional
studies (such as those conducted by USGS) are important for documenting the status and trends
of groundwater availability, as these trends affect local groundwater resources, particularly when
changes in an aquifer occur beyond the local or state political boundaries.38

36 C. C. Faunt et al., Groundwater Availability of the Central Valley Aquifer, California, USGS, USGS Professional
Paper 1766, 2009, at https://pubs.usgs.gov/pp/1766/.
37 James A. Miller et al., Ground Water Atlas of the United States, USGS, 2000, at https://water.usgs.gov/ogw/aquifer/
atlas.html.
38 See, for example, K. F. Dennehy, T. E. Reilly, and W. L. Cunningham, “Groundwater Availability in the United
States: The Value of Quantitative Regional Assessments,” Hydrogeology Journal, vol. 23, no. 8 (December 2015), pp.
Congressional Research Service

14

link to page 19
The Federal Role in Groundwater Supply

NASA
Earth-observing satellites can provide information to assess changes in the amount of
groundwater stored in large aquifers, variations in the amount of soil moisture, and tiny
fluctuations in land elevation that reflect how the water table is moving up and down.
Using data from NASA’s GRACE and SMAP satellites,39 integrated with other observations,
scientists can analyze shallow groundwater and soil moisture levels that reflect drought
conditions across the United States (Figure 8).
Figure 8. Shallow Groundwater and Soil Moisture Comparison from NASA Satellite
Data

Source: The National Drought Mitigation Center, “Groundwater and Soil Moisture Conditions from GRACE
Data Assimilation,” at http://nasagrace.unl.edu/Default.aspx. (Modified by CRS.)
Notes: Map shows wet or dry conditions relative to the probability of occurrence using the baseline period
from 1948 to 2012, expressed as a percentile. The lower values in the warmer colors indicate drier-than-normal
conditions (30th percentile or less), and the cooler colors indicate wetter-than-normal conditions (70th percentile
or more). Areas in white express 31st-69th percentile, spanning the midpoint of 50th percentile (the 50th
percentile indicates that half the values are higher and half are lower). The map is available for the contiguous
United States from the data source and does not include Alaska and Hawaii.
Data from the GRACE satellite also have been interpreted to show changes in the amount of
groundwater held in storage in large, regional aquifers, such as the Central Valley aquifer in
California, the High Plains aquifer underlying several states in the Midwest and Great Plains, and

1629-1632; and Roland Barthel, “A Call for More Fundamental Science in Regional Hydrogeology,” Hydrogeology
Journal
, vol. 22, no. 3 (May 2014), pp. 507-510.
39 GRACE stands for Gravity Recovery and Climate Experiment satellite (see https://www.nasa.gov/mission_pages/
Grace/index.html); SMAP stands for Soil Moisture Active Passive satellite (see https://smap.jpl.nasa.gov/).
Congressional Research Service

15

The Federal Role in Groundwater Supply

other large aquifers around the world.40 One study using GRACE data indicated that the volume
of groundwater in the Central Valley aquifer pumped out over a 78-month period was equivalent
to nearly the capacity of Lake Mead.41
Scientists can use a special type of radar data collected by satellites using a technique called
synthetic aperture radar interferometry to detect minute changes in the land-surface elevation
caused when the water table moves up and down. In one study, NASA scientists and others used
the technique to track how the aquifer in the Santa Clara Valley, California, recovered following
depletion during a drought when conservation measures were put in place to limit groundwater
pumping.42 In that study, a cluster of Italian satellites provided the radar data. NASA is planning a
joint mission with the Indian Space Research Organisation in 2021 that would collect radar
imagery of nearly every major aquifer in the world.43
NOAA
NOAA coordinates and integrates drought research and forecasting from federal, state, tribal,
local, and academic sources through the National Integrated Drought Information System. NOAA
uses data from these and other sources to create drought maps, seasonal outlooks, and other
drought indicators, including effects of drought on groundwater.44 A typical U.S. Drought
Monitor map, for example, indicates which regions of the country are experiencing short- and
long-term impacts from drought. Long-term-impacted regions mean that drought has affected the
region’s hydrology, including groundwater resources.
NOAA’s constellation of both geostationary and polar-orbiting weather satellites provides real-
time atmospheric weather data that can be used to better understand the hydrologic cycle in
regions across the country. The satellite data contribute to short- and long-term forecasts of
precipitation that, for example, can inform groundwater models and other tools about water
available for groundwater recharge. NOAA data from satellites and ground-based observing
systems also feed into longer-term climate forecasts and climate models, which can be used to
help understand the potential effects of climate change on groundwater supplies.
USDA
The Census of Agriculture is required by law and authorizes the Secretary of Agriculture to
conduct surveys deemed necessary to furnish annual or other data on the subjects covered by the
census.45 The census is a broad survey that includes questions about irrigation and water use, and
is conducted every five years. A more detailed national assessment of irrigated agriculture in the

40 See, for example, NASA, Jet Propulsion Laboratory, “GRACE Tellus: Groundwater,” at https://grace.jpl.nasa.gov/
applications/groundwater/.
41 About 31 cubic kilometers, or 6.8 trillion gallons. See J. S. Famiglietti et al., (2011), Satellites Measure Recent Rates
of Groundwater Depletion in California’s Central Valley
, Geophys. Res. Lett., 38, L03403, at
doi:10.1029/2010GL046442.
42 Estelle Chaussard et al., “Remote Sensing of Ground Deformation for Monitoring Groundwater Management
Practices: Application to the Santa Clara Valley During the 2012-2015 California Drought,” Journal of Geophysical
Research-Solid Earth
, vol. 122, no. 10 (September 21, 2017), pp. 8566-8582.
43 See, for example, NASA, Jet Propulsion Laboratory, “Satellites See Silicon Valley’s Quick Drought Recovery,”
October 3, 2017, at https://www.jpl.nasa.gov/news/news.php?feature=6962.
44 See National Integrated Drought Information System (NIDIS), “What Is NIDIS?,” at https://www.drought.gov/
drought/what-nidis.
45 7 U.S.C. 2204g et seq.
Congressional Research Service

16

link to page 22 link to page 6 The Federal Role in Groundwater Supply

United States is the Irrigation and Water Management Survey (formally the Farm and Ranch
Irrigation Survey), also conducted every five years, and usually two or three years after the
general census and under the same authority.46 The most recent Irrigation and Water Management
Survey (2018), conducted by the National Agricultural Statistics Service in USDA, supplemented
the basic irrigation data collected from all farm and ranch operators in the 2017 census.47
Federal Authority Related to Groundwater Recharge, Storage, and
Recovery
Recharging groundwater artificially with surface water is not a new concept, but interest in the
practice is growing at the local, state, and federal levels for several reasons. When surface water
supplies are curtailed because of drought, diversion for other uses, regulatory constraints, or other
reasons, groundwater is often used to meet the demand. In addition, if demand for water supplies
increases and additional surface water is not available, consumers may turn to groundwater.
Along the coastline, groundwater extraction and the lowering of the water table sometimes have
resulted in saltwater intrusion into the aquifer. Groundwater recharge may be used in those cases
to replenish the aquifer and create a freshwater barrier to prevent seawater encroachment.
Groundwater recharge, storage, and recovery also may be part of a conjunctive water
management strategy in which both surface and groundwater are used, recharging groundwater in
times of surface water surplus and extracting groundwater when surface water is in short supply.
Typically, groundwater recharge, storage, and recovery involves either injecting water into the
aquifer through a well or allowing water to recharge from an impoundment (e.g., a pond) or a
spreading basin (water is spread on the ground to percolate down to the aquifer). The water is
stored in the aquifer until it is recovered by a pumping well for freshwater supply. Figure 9
illustrates the process.

46 For more information on the most recent Irrigation and Water Management Survey, see U.S. Department of
Agriculture, Census of Agriculture, “2018 Irrigation and Water Management Survey,” at https://www.nass.usda.gov/
Publications/AgCensus/2017/Online_Resources/Farm_and_Ranch_Irrigation_Survey/index.php.
47 The USDA Irrigation and Water Management Survey differs from the USGS water use estimates report in
methodologies and reporting schedules and should not be compared directly. See footnote 6.
Congressional Research Service

17


The Federal Role in Groundwater Supply

Figure 9. Groundwater Recharge, Storage, and Recovery

Source: National Groundwater Association (NGWA), “Managed Aquifer Recharge: A Water Supply
Management Tool,” NGWA Information Brief, 2014 (with permission). (Modified by CRS.)
Notes: The figure shows how the aquifer is recharged using a recharge well (on the right) and from recharge
basins (middle of the figure). The recharge well is recharging a confined aquifer, and the recharge basins are
recharging an unconfined aquifer.
According to several sources, more than 1,000 aquifer recharge wells and aquifer storage and
recovery wells, along with many recharge basins, have been constructed across the nation.48 In
addition to technical, economic, and regulatory issues, identifying and providing a source of
water for these activities is critical. Increasingly, federal water resource projects, such as those
managed by Reclamation and USACE, are being considered as potential sources of recharge
water. Reclamation, USDA, and EPA are also potential sources of financial assistance for
supporting aquifer recharge, storage, and recovery projects. This section identifies various federal
authorities for groundwater storage, recharge, and recovery.
Bureau of Reclamation
Reclamation, a federal agency of the Department of the Interior, owns and operates hundreds of
dams and water diversion structures projects in the 17 coterminous U.S. states west of the
Mississippi River. Reclamation was created by Congress in the Reclamation Act of 1902,49 which
authorized the Secretary of the Interior to construct irrigation works in western states. In addition
to water supply, Reclamation facilities also provide flood control, recreation, and fish and wildlife
benefits.50 Reclamation cites several authorities for groundwater activities, including the authority
to deliver project and excess water for aquifer storage and recharge and the authority to provide
financial support for these activities. These authorities are discussed below.

48 See, for example, U.S. Environmental Protection Agency, Underground Injection Control, “Aquifer Recharge and
Aquifer Storage and Recovery,” at https://www.epa.gov/uic/aquifer-recharge-and-aquifer-storage-and-
recovery#inventory; and National Groundwater Association, “Aquifer Storage and Recovery: Need for Critical
Analysis of the Technical, Economic, and Regulatory Issues,” at http://www.ngwa.org/Media-Center/issues/Pages/
Aquifer-storage-and-recovery.aspx.
49 Act of June 17, 1902 (ch. 1093, 32 Stat. 388).
50 For a brief synopsis of Reclamation project authorization and financing, see CRS In Focus IF10806, Bureau of
Reclamation Project Authorization and Financing
, by Charles V. Stern.
Congressional Research Service

18

The Federal Role in Groundwater Supply

Reclamation Authority to Deliver Project or Excess Water for Groundwater Use
Overall, Reclamation reports no federal restrictions on its authority to deliver project or excess
water to contractors for groundwater recharge, and contractors using these waters for groundwater
recharge are not required to seek any special approvals beyond what is normally required by
Reclamation. However, DOI officials also have acknowledged that Reclamation’s existing
authorities for groundwater use are general in nature, and increased specificity of these authorities
may be useful.51 For example, some aquifers underlie both project and non-project areas, with
non-project areas being the preferable delivery location for groundwater uses due to one or more
factors (e.g., land use, geology). However, under Reclamation’s existing authorities, the delivery
of “project waters” (i.e., waters for which Reclamation holds water rights) for groundwater uses
may be limited to lands within a Reclamation project’s authorized boundaries. As a result, some
have urged Congress to clarify Reclamation authorities to deliver project water for groundwater
recharge outside of project boundaries.52 Reclamation also reports that some state restrictions
affect the use of these waters for groundwater activities. In general, Reclamation does not track
the use of project or excess water for groundwater recharge, although these uses appear to be
occurring in at least a few places. The following authorities have been or may be used by
Reclamation for groundwater storage:
 Section 9 of the Reclamation Project Act of 1939 (43 U.S.C. §485) is the general
authority by which Reclamation is authorized to enter into contracts to furnish
water for irrigation, municipal, and miscellaneous water supply purposes.
Reclamation interprets the purposes of deliveries under this section to include
groundwater recharge.
 Section 1 of the Warren Act of February 21, 1911 (43 U.S.C. §523), authorizes
Reclamation to enter into contracts for the conveyance and storage of non-project
water through the federal reclamation project, when the water is to be used for
irrigation purposes and excess capacity exists. This authority has in some cases
been used for groundwater recharge.53
 Section 215 of the Reclamation Reform Act of 1982 (P.L. 97-293) is the authority
Reclamation uses to enter into temporary water service contracts for un-storable
or excess flood flows. Reclamation indicates that it has no restrictions on using
these waters for groundwater recharge.
 Section 101(d) of the Reclamation States Emergency Drought Relief Act of 1991
(P.L. 102-250) authorizes Reclamation to participate in state-established water
banks
to respond to drought.54

51 Statement of Timothy Petty, Assistant Secretary for Water and Science, U.S. Department of the Interior, before the
U.S. Congress, Senate Committee on Energy and Natural Resources, Full Committee Hearing to Examine the 2018
Western Water Supply Outlook and Bills Related to Water Infrastructure and Drought Resiliency
, 115th Cong., 2nd
sess., March 22, 2018.
52 See, for example, U.S. Congress, Senate Committee on Energy and Natural Resources, Aquifer Recharge Flexibility
Act
, Report to Accompany S. 1570, 116th Cong., 1st sess., October 29, 2019, S.Rept. 116-155 (Washington: GPO,
2019). Hereinafter, “S. Rept. 116-155.”
53 In its report accompanying S. 1570, the Aquifer Recharge Flexibility Act, the Senate Committee on Energy and
Natural Resources noted that the ability to enter into a Warren Act contract for